<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>
<div>
    <input type="text" id="input">
    <div>内容：<span id="span"></span></div>

</div>
</body>
<script src="实现一个双向数据绑定.js"></script>
</html>